To establish whether chromatographically unique tRNAs formed in E. coli during inhibition of protein synthsis are modification deficient precursor tRNAs or products of tRNA genes not normally expressed and the biochemical basis of this phenomenon. Base compositional, fragment, and hybridization analyses of a normal and unique tRNAphe will be performed. To determine the size of the tRNA gene clusters in E. coli DNA and if such clusters also occur in bacteriophage T5 DNA. Isotopically labeled tDNA fragments (complementary to tRNA) of different size will be isolated and hybridized with radioactive tRNA. The ratio of tRNA:DNA in the resulting hybrids will be determined by density gradient and column fractionation methods. To determine the biological activity of modification deficient precursor tRNAs derived from amino acid starved RC minus E. coli and from in vitro transcription of bacteriophage phi 80 su3 plus DNA. The RC minus tRNAs will be tested for the ability to translate a natural mRNA while an in vitro suppression assay will be used to test the putative su3 plus tyrosine tRNA precursors from phi 80 su3 plus DNA.